The Optical Transport Network (OTN) is a network technology for the transport of optical data signals at very high rates (2, 5, 10, and 40 Gbit/s). OTN relies on time division multiplexing of constant rate transport signals to even higher rate transport signals and supports wavelength division multiplexing, as well. Signal structures and interfaces of the Optical Transport Network have been defined in ITU-T G.709 (03/2003), which is incorporated by reference herein.
Control plane technologies based on the GMPLS protocol family have been introduced to allow automated path setup through the network. Traditionally, creating traffic paths through a series of network elements has involved configuration of individual cross-connections on each network element. In an Automatic Switched (Optical) Transport Network (ASTN or ASON), just the start point, end point and bandwidth required needs to be specified through the user, and the control plane of the network will automatically allocate the path through the network, provision the traffic path, set up cross-connections, and allocate bandwidth from the paths for a client signal.
In order to support such automatic path creation through control plane signaling, a protocol for automatic discovery of layer adjacencies in the transport plane has been defined in ITU-T G.7714.1(04/2003), which is incorporated by reference herein. Layer Adjacency Discovery (LAD) describes the process of discovering the link connection end-point relationships and verifying their connectivity. The term “discovery” is used in this context to refer to both “discovery” and verification. G.7714.1 defines two alternative methods: one using a test set in the client layer, the other using in-band overhead in the server layer.
In particular, G.7714.1 defines under its chapter 6 the following mechanisms as applicable to the OTN layer networks:                OTUk layer: Within the OTUk layer the SM section monitoring byte and the GCC0 may be used to support discovery of the OTUk adjacency. Specifically, the SAPI subfield within the SM is used to carry the discovery message.        ODUk layer: Within the ODUk layer the PM path monitoring byte and the GCC1 and GCC2 bytes may be used to support discovery of the ODUk adjacency. Specifically, the SAPI subfield within the PM is used to carry the discovery message.        
The present invention aims at improving this automatic discovery mechanism.